Patterns of Thyroid-Stimulating Hormone Test After GLP-1 RAs Initiation in Patients on Levothyroxine: A Trial Emulation Study.

Abstract

GLP-1 RAs are widely prescribed for type 2 diabetes and obesity and can lead to substantial weight loss. In patients taking levothyroxine, weight loss can reduce thyroid hormone requirements, potentially associated adverse effects. TSH monitoring is essential but unclear whether thyroid function is routinely reassessed after GLP-1 RAs initiation. Examine the changes in the timing of TSH testing after GLP-1 RAs. Retrospective cohort study emulating a target trial using Medicare from January 1, 2011, to December 31, 2020. The primary analysis followed an intention-to-treat approach. Patients were matched 1:1 using propensity scores. Logistic regression models and informed by LASSO variable selection were used. The 15% sample of U.S. Medicare fee-for-service claims data. Adults aged ≥65 years with type 2 diabetes on a stable levothyroxine dose at baseline. Initiation of GLP-1 RAs versus initiation/ongoing use of SGLT-2is. TSH testing during follow-up. Among 5,370 matched patients, the mean age was 73.2 years. 71.6% were women, and 87.1% were White. Approximately 83.0% of patients in both treatment groups receive a TSH testing within a 1-year follow-up. The mean time to TSH testing was approximately 130.5 days for both groups. TSH testing patterns did not differ between GLP-1 RAs and SGLT-2is, despite the greater likelihood of requiring levothyroxine dose adjustment associated with weight loss seen with GLP-1 RAs therapy. Given levothyroxine's widespread use, this gap suggests missed opportunities for timely and weight-responsive thyroid monitoring.